# std::flat_set<Key,Compare,KeyContainer>::find

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< cpp‎ | container‎ | flat set

iterator find( const Key& key ); | (1) | (since C++23)
const_iterator find( const Key& key ) const; | (2) | (since C++23)
template< class K > iterator find( const K& x ); | (3) | (since C++23)
template< class K > const_iterator find( const K& x ) const; | (4) | (since C++23)

1,2) Finds an element with key equivalent to key.
3,4) Finds an element with key that compares equivalent to the value x. This overload participates in overload resolution only if the qualified-id Compare::is_transparent is valid and denotes a type. It allows calling this function without constructing an instance of `Key`.

### Parameters

key | - | key value of the element to search for
x | - | a value of any type that can be transparently compared with a key

### Return value

An iterator to the requested element. If no such element is found, past-the-end (see end()) iterator is returned.

### Complexity

Logarithmic in the size of the container.

### Example

Run this code

    #include <iostream>
    #include <flat_set>

    struct LightKey
    {
        int x;
    };

    struct FatKey
    {
        int x;
        int data[1000]; // a heavy blob
    };

    // As detailed above, the container must use std::less<> (or other transparent
    // Comparator) to access these overloads. This includes standard overloads,
    // such as comparison between std::string and std::string_view.
    bool operator<(const FatKey& fk, const LightKey& lk) { return fk.x < lk.x; }
    bool operator<(const LightKey& lk, const FatKey& fk) { return lk.x < fk.x; }
    bool operator<(const FatKey& fk1, const FatKey& fk2) { return fk1.x < fk2.x; }

    int main()
    {
        // Simple comparison demo.
        std::flat_set<int> example{1, 2, 3, 4};

        if (auto search = example.find(2); search != example.end())
            std::cout << "Found " << (*search) << '\n';
        else
            std::cout << "Not found\n";

        // Transparent comparison demo.
        std::flat_set<FatKey, std::less<>> example2{{1, {}}, {2, {}}, {3, {}}, {4, {}}};

        LightKey lk = {2};
        if (auto search = example2.find(lk); search != example2.end())
            std::cout << "Found " << search->x << '\n';
        else
            std::cout << "Not found\n";
    }

Output:

    Found 2
    Found 2

### See also

count | returns the number of elements matching specific key (public member function)
equal_range | returns range of elements matching a specific key (public member function)

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